Objective To assess the feasibility, acceptability, and preliminary effectiveness of digital peer support integrated medical and psychiatric self-management intervention (“PeerTECH”) for adults with a serious mental illness. Methods Twenty-one adults with a chart diagnosis of a serious mental illness (i.e., schizophrenia, schizoaffective disorder, bipolar disorder, or treatment-refractory major depressive disorder) and at least one medical comorbidity (i.e., cardiovascular disease, obesity, diabetes, chronic obstructive pulmonary disease, hypertension, and/or high cholesterol) aged 18 years and older received the PeerTECH intervention in the community. Nine peer support specialists were trained to deliver PeerTECH. Data were collected at baseline and 12-weeks. Results This pilot study demonstrated that a 12-week, digital peer support integrated medical and psychiatric self-management intervention for adults with serious mental illness was feasible and acceptable among peer support specialists and patients and was associated with statistically significant improvements in self-efficacy to manage chronic disease and personal empowerment. In addition, pre/post non-statistically significant improvements were observed in psychiatric self-management, medical self-management skills, and feelings of loneliness. Conclusions This single-arm pre/post pilot study demonstrated preliminary evidence peer support specialists could offer a fidelity-adherent digital peer support self-management intervention to adults with serious mental illness. These findings build on the evidence that a digital peer support self-management intervention for adults with serious mental illness designed to improve medical and psychiatric self-management is feasible, acceptable, and shows promising evidence of improvements in clinical outcomes. The use of technology among peer support specialists may be a promising tool to facilitate the delivery of peer support and guided evidence-based self-management support. People with serious mental illness (SMI; defined as individuals diagnosed with schizophrenia spectrum disorder, bipolar disorder, or treatment-refractory major depressive disorder) are increasingly utilizing peer support services to support their health and recovery. Peer support is defined as shared knowledge, experience, emotional, social, and/or practical assistance to support others with similar lived experiences (Solomon, 2004). Most recently the definition also includes the provision of evidence-based peer-supported self-management services (Fortuna et al., 2020). Mental health peer support can augment the traditional mental health treatment system through providing support services to maintain recovery between clinical encounters (Solomon, 2004) and is classified by the World Health Organization as an essential element of recovery (World, Health, and Organization, About social determinants of health, 2017).